Fluctuations of conserved charges, like baryon number, electric charge and strangeness, are generally considered to be sensitive indicators for the structure of a thermal medium produced in heavy ion collisions [1]}.
Under conditions met in current experiments at RHIC as well as in the upcoming heavy ion experiments at LHC the net baryon number is small and QCD at vanishing chemical potential provides a good approximation.
In this region the transition from the low temperature hadronic to the high temperature plasma regime is continuous and fluctuations are not expected to lead to any singular behavior. Indications for the existence of critical points can only show up in higher order derivatives of the QCD partition function with respect to temperature or chemical potentials [2]}. Through the analysis of fluctuations of conserved charges as well as their higher moments and correlations we thus gain insight into the relevant degrees of freedom of the system under consideration and at the same time gather information on possible nearby singularities in the QCD phase diagram.
